Try to look again on AOL, if you still have access, and look for Achive folder, the very old mails may be there.
Of course, you can also ask their support without mentioning Bitcoin, but if they get too curious and your info is not encrypted / password-protected they may help themselves...
Google about recovering old AOL mails.

Also one copy of those mails could be locally, but I don't know if, how and by what rules. Maybe it would not hurt to make a clone all those old computers' HDDs and keep one set of copies untouched, or at least not use for a while those HDDs. And of course, start digging for whatever could be useful - maybe wallet.dat files, maybe zip or rar files in case you archived them and of course old mails saved in whatever form.

PS. If you talk about thousands of Bitcoin, I an surprised that you ignored them in 2014 and 2017...